Several types of prior art dispensing systems are used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards and integrated circuit chips, wherein dispensing systems are used in the process of encapsulating integrated circuits with an encapsulant material and in the process of under filling flip integrated circuit chips with an encapsulant. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards and integrated circuits. The liquid epoxy and solder is primarily used to connect components to a circuit board or to connect components within an integrated circuit. The dispensing systems described above include those manufactured and distributed by Camelot Systems, Inc. of Haverhill, Mass., the assignee of the present invention under the name CAM/ALOT.RTM..
In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z), by servomotors controlled by a computer system or controller. To dispense a volume of liquid on a circuit board or some other substrate at a desired location, the pump and dispenser assembly is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z axis until the nozzle is at an appropriate height over the substrate. The pump and dispenser assembly dispenses a predetermined volume of liquid, is then raised along the z axis, moved along the x and y axes to a next desired location, and is lowered along the vertical z axis to dispense the predetermined volume of liquid at the next location.
In dispensing applications such as those described above, the accuracy of the volume of liquid dispensed by the system is an important feature of the system. In one prior art dispensing system, the pump and dispenser assembly includes an auguring screw housed in an auguring chamber within a dispenser housing. The auguring screw is rotated within the chamber to provide a controlled amount of liquid. The pump and dispenser assembly has a nozzle for dispensing material onto a substrate. The liquid to be dispensed by the pump and dispenser assembly is contained in a vertical, cylindrical syringe coupled to the dispenser housing by a bracket. The syringe has a top piece having clamps that provide a pressure tight seal between the syringe and the top piece. The top piece includes an adapter for coupling to an air line to receive pressurized air. The pressurized air is used to force the dispensing material from the syringe into the pump and dispenser assembly.
The prior art dispensing systems described above are effective in dispensing material onto a substrate, however, it is desirable to have a dispensing system having greater precision in controlling the amount of material to be dispensed.